Fast switching immobilized photochromic dyes

Article abstract of DOI:10.1002/pola.24461

A novel photochromic dye conjugate architecture is described, which allows both covalent tethering to a polymeric host matrix and fast photochromic switching. The new conjugates consist of a photochromic dye covalently bound to two different substituents

Full text of DOI:10.1002/pola.24461

Fast Switching Immobilized Photochromic Dyes
NINO MALIC,1,2 JONATHAN A. CAMPBELL,2,3 ABDELSELAM S. ALI,1 CRAIG L. FRANCIS,1 RICHARD A. EVANS1,2,3
1CSIRO Materials Science and Engineering, Bag 10, Clayton, Victoria 3169, Australia
2The Cooperative Research Centre for Polymers, 8 Redwood Drive, Notting Hill, Victoria 3168, Australia
3School of Chemical Sciences and Engineering, The University of New South Wales, Sydney, New South Wales 2052, Australia
Received 30 September 2010; accepted 25 October 2010
DOI: 10.1002/pola.24461
Published online 29 November 2010 in Wiley Online Library (wileyonlinelibrary.com).
ABSTRACT: A novel photochromic dye conjugate architecture is
described, which allows both covalent tethering to a polymeric
host matrix and fast photochromic switching. The new conju-
gates consist of a photochromic dye covalently bound to two
different substituents via a Y-branching linker (hetero Y-branch-
ing), one being a polymerizable methacrylate moiety and the
other a soft (low Tg) poly(dimethylsiloxane) oligomer. The
novel conjugates gave faster photochromic decoloration in the
host lens matrix compared with the electronically equivalent
nonmatrix-bound and unconjugated parent control dyes. In
addition, further acceleration of fade speed kinetics was
observed with a longer linker between photochromic dye and
C
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methacrylate moiety.
2010 Wiley Periodicals, Inc. J Polym
Sci Part A: Polym Chem 49: 476–486, 2011
KEYWORDS: branched; matrix; photochromic dyes; polydime-
thylsiloxane; polysiloxanes; tethering; Y-branched
INTRODUCTION Photochromic dyes are light-responsive mol-
ecules, which undergo a reversible change in color when
exposed to UV radiation (Fig. 1)1 and have found application
in photoresponsive systems leading to the development of
smart materials.2 For many types of photochromic dyes this
color change is accompanied by large structural transforma-
tions, where one half of the molecule undergoes a mechani-
cal rotation with respect to the other.3 Such a large intramo-
lecular rotation renders these molecules quite sensitive to
the viscosity of their local environment. Certainly within
rigid polymeric matrices, a dramatic slowing of coloration
and decoloration kinetics is seen when compared with solu-
tion speeds.3–5 A reduced free volume and lack of fluidity
within such matrices hinder the mechanics of photochrom-
ism resulting in slowing of switching speeds, known as the
matrix effect.6 The use of photochromic dyes within the oph-
thalmic industry is well known.7 To this day the industry is
still faced with the challenge of overcoming the conflicting
demands of faster photochromic dye performance and lens
rigidity, for mechanical properties such as shatter-proofing
and scratch resistance.
leads to a change in its coloration and decoloration kinetics
due to the different local viscosities of the former environ-
ment versus the latter. This would lead to an overall compro-
mised color performance of the lens product over time, par-
ticularly where several different dyes are used to achieve
neutral colors of grey or brown. However, the tethering of
photochromic dyes directly to a polymer is known to further
decrease coloration and decoloration speeds beyond that of
dyes which are simply dispersed within the matrix.3 It has
been shown that some modulation of fade speed is achieva-
ble (as well as modulation of the trans–cis isomerization
within an azobenzene photochromic polymer)9 via changes
in the length of the linker between the dye and the polymer
backbone, with longer linkers providing faster fade per-
formance.3,9–13 The notion is that longer linkers isolate the
photochromic dye from the steric influences of the main
polymer chain, which hinder the mechanical processes of
photochromism.
We have recently developed a technology that provides a
means to increasing coloration and decoloration kinetics of
photochromic dyes within rigid polymeric lens matrices
through polymer conjugation.5,14–18 The covalent attachment
of soft (low Tg) polymers to photochromic dyes provides a
lubricating environment immediately surrounding the dye,
thus allowing relatively unhindered intramolecular rotation
during photochromic switching without compromising the
mechanical properties (hardness and rigidity, which are nec-
essary for scratch and impact resistance) of the matrix. Such
Current commercial photochromic lens products generally
contain dyes which are freely incorporated within the lens
matrix or coating. However, in certain circumstances, it may
be advantageous to have the dye covalently bound to the
matrix, thus preventing migration which can lead to deterio-
ration in performance of the individual dye components.8
For example, migration of a dye molecule to an interface
Correspondence to: R. A. Evans (E-mail: richard.evans@csiro.au)
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Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 49, 476–486 (2011) 2010 Wiley Periodicals, Inc.
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FIGURE 1 Transition between
colorless to colored forms in a
spirooxazine and naphthopyran
photochromic
dye,
showing
redistribution of double bonds
and intramolecular rotation.
conjugates have thus far been simply dispersed throughout the
host matrix. This article now describes a method by which
photochromic dyes may be covalently bound to a rigid host
polymeric matrix with the added ability for fast switching.
values of SiCH2 resonances along the backbone with respect
to those of Si(CH3)2. Final molecular weights of dye–PDMS
conjugates were additionally confirmed from integration of
characteristic dye end groups. Photochromic analyses were
performed on lenses containing photochromic materials at
doping concentrations chosen to maintain optical densities
in a meaningful detector range during photochromic kinetic
tests (Table 2). The fabrication and composition of test
lenses is outlined within the main body text. Under continu-
ous irradiation, the photochromic responses of the lenses
were analyzed on a light table comprising a Cary 50 UV–Vis
spectrophotometer to measure absorbance values and a 160
W Oriel xenon lamp as an incident light source. A series of
two filters (Edmund Optics WG320 and Edmund Optics
band-pass filter U-340) were used to restrict the output of
the lamp to a narrow band (350–400 nm). The samples
were maintained at 20 ꢀC and monitored at the maximum
absorbance of their colored form for a period of 1000 s.
Then the thermal decoloration was monitored in the dark
for a further 2400 s (minimum).
We have developed a novel conjugate architecture comprised
of a photochromic dye covalently bound to a hetero-function-
alized Y-branching linker. One of these functionalities is a
polymerizable methacrylate moiety while the other is a
poly(dimethylsiloxane) (PDMS) oligomer whose purpose is
to allow fast photochromic switching in a rigid lens matrix
by providing a soft and fluid local environment (Fig. 2).
Examples of such conjugates synthesized for this study are
shown in Table 1 (spirooxazine compounds 7 and 8) and
Table 2 (naphthopyran compound 13).
EXPERIMENTAL
Materials and Methods
Hydroxy-terminated PDMS starting materials were purchased
from Gelest. All other reagents were purchased from Aldrich
and used as supplied, unless stated otherwise. 90-Hydroxy-
1,3,3-trimethylspiro[indoline-2,30-[3H]naphth[2,1-b][1,4]oxazine]19
and 2-phenyl-2-(4-dimethylaminophenyl)-5-hydroxymethyl-7,9-
dimethoxy-2H-naphtho[1,2-b]pyran20 were synthesized by the
literature procedures. Spirooxazine propionate derivative, 6,
was synthesized using the patent procedure.21
General Experimental Measurements
1H (400 MHz/200 MHz) and 13C (100 MHz/50 MHz) NMR
spectra were obtained with a Bruker AV400 or a Bruker
AC200 spectrometer at 25 ꢀC. Spectra were recorded for
samples dissolved in deuterated solvent and chemical shifts
are reported in parts per million from external tetramethylsi-
lane and J values are given in Hz. Molecular weights of
PDMS were obtained from 1H NMR spectra from integration
FIGURE 2 Novel hetero Y-branched photochromic dye conju-
gates incorporating methacrylate functionality for matrix teth-
ering and a soft poly(dimethylsiloxane) oligomer for enhancing
photochromic performance (coloration and decoloration)
within a rigid polymeric matrix.
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TABLE 1 Spirooxazine-Functionalized Conjugates and Control Compounds
Compound
Structure
Spirooxazine Monomethacryloyloxyethyl
Succinate, 5
Step 1
in vacuo with the aid of dichloromethane. This afforded
mono-2-(methacryloyloxy) ethyl succinoyl chloride, as a light
yellow oil in quantitative yield, which was used immediately
in the next step.
Mono-2-(methacryloyloxy)ethyl succinate (0.60 g, 2.61
mmol) was dissolved in dry dichloromethane (8 mL) in a
dry Schlenk flask under nitrogen. Dimethylformamide (DMF)
(one small drop) was added via syringe followed by oxalyl
chloride (0.46 mL, 5.21 mmol) in one portion. The mixture
was stirred at room temperature for 30 min. The solvent
and the majority of excess oxalyl chloride were removed by
evaporation in vacuo, with the residual reagent removed
Step 2
Triethylamine (0.11 g, 0.15 mL, 1.09 mmol) was added to a
suspension of 90-hydroxy-1,3,3-trimethylspiro[indoline-2,30-
[3H]naphth[2,1-b][1,4]oxazine (0.25 g, 0.73 mmol) in dry
CH2Cl2 (10 mL) under a nitrogen atmosphere. Mono-2-
(methacryloyloxy)ethyl succinoyl chloride (0.181 g, 0.73
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TABLE 2 Naphthopyran-Functionalized Conjugates and Control Compounds
Compound Structure
mmol) was added dropwise and the mixture was stirred at
room temperature for 30 min. The solvent was evaporated
in vacuo, and the residue was purified by column chromatog-
raphy (silica gel, Et2O/hexane, 4:1) to give the product as a
green solid (0.393 g, 97%).
Step 1
Monohydroxyl end-terminated PDMS S1 (25 g, ca. 22.1
mmol) and succinic anhydride (2.65 g, 26.5 mmol) were
added to dry CH2Cl2 (ca. 30 mL) under nitrogen. Triethyl-
amine (3.35 g, 4.61 mL, 33.1 mmol) was added in one
portion and the mixture was stirred at room temperature for
30 min followed by heating at 35 ꢀC for 1 h. Polyethylene
glycol (PEG) methyl ether (3.86 g, 11.0 mmol) was added
and the mixture was stirred for an additional 30 min at 35
ꢀC. It was then poured into hexane, washed with several por-
tions of 2 M HCl; the organic layer was dried with MgSO4
and the solvent was evaporated to give the pure product as
a colourless oil (26.34 g, 97%). Comments: An excess of suc-
cinic anhydride is used to drive the reaction to completion.
The removal of the remaining anhydride is facilitated by its
reaction with PEG methyl ether, resulting in a very polar
product which is easily extracted with water. This procedure
gives a pure product in high yield without the need for fur-
ther purification.
1H NMR (200 MHz, d6-acetone) d 8.25 (d, 1H), 7.88 (d, 1H)
7.83 (s overlap, 1H), 7.81 (d overlap, 1H), 7.13–7.22 (m, 3H),
7.04 (d, 1H), 6.87 (m, 1H), 6.66 (d, 1H), 6.08 (m, 1H), 5.61 (m,
1H), 4.41 (m, 4H), 3.00 (m, 2H), 2.81 (m overlap, 2H), 2.75 (s
overlap, 3H), 1.90 (m, 3H), 1.36 (s, 3H), 1.34 (s, 3H) ppm.
Spirooxazine Hetero Y-Branched
(Poly(dimethylsiloxane)/methacrylate) Conjugate,
7, and Spirooxazine Methacrylate, 4
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1H NMR (400 MHz, CDCl3) d 4.25 (t, J ¼ 4.76 Hz, 2H, CH2-3),
3.63 (t, J ¼ 4.76 Hz, 2H, CH2-4), 3.42 (t, J ¼ 7.32 Hz, 2H,
CH2-5), 2.67 (s, 4H, CH2-1,2), 1.61 (m, 2H, CH2-6), 1.31 (m,
4H, CH2-9,10), 0.88 (t, J ¼ 6.95 Hz, 3H, CH3-11), 0.53 (m, 4H,
CH2-7,8), 0.07 (s, approx. 80H, SiCH3) ppm.
eluting first. Several fractions were collected here, each having
different average molecular weight values. Average molecular
weights of the pure product fractions collected were deter-
mined by 1H NMR (integration of SiCH3 signals of PDMS vs.
end functionality). Various fractions of this product compound
2 were used in the synthesis steps which follow from hereon.
1H NMR (400 MHz, CDCl3) d 4.33–4.23 (m, 4H), 3.67 (m,
4H), 3.47 (t, 2H), 2.65 (s, 4H), 1.63 (m, 2H), 1.31 (m, 4H),
1.22 (s, 3H), 0.87 (t, 3H), 0.53 (m, 4H), 0.06 (m, SiCH3) ppm.
Step 2
Compound S2 (1.00 g, ca. 0.81 mmol) was dissolved with stir-
ring in dry CH2Cl2 (10 mL) under argon, and dimethylforma-
mide (one drop) was added. The mixture was cooled in an ice
bath and then oxalyl chloride (0.41 g, 0.28 mL, 3.24 mmol) was
ꢀ
added in one portion. Stirring was continued at 0 C for 15 min
and then at room temperature for 20 min while maintaining a
slow argon flow above the reaction by means of a syringe needle
through a rubber septum.22 The solvent and excess reagent
were removed by evaporation in vacuo and the residual reagent
was further removed in vacuo with the aid of 1,2-dichloroethane.
The acid chloride product S3 was used immediately. Analysis
by 1H NMR in d-chloroform showed quantitative conversion.
Comments: It is important that the reaction duration be no
longer than 30 min at room temperature. Significant amounts
of by-products are formed at longer reaction times and when
more forcing conditions are used (i.e., elevated temperatures).
Step 4
Methacryloyl chloride (0.16 mL, 1.65 mmol) was added drop-
wise to a stirred solution of compound 2 (1.18 g, 0.75 mmol),
triethylamine (0.31 mL, 2.25 mmol), and 4-dimethylaminopyri-
dine (1-2 mg) in CH2Cl2 (8 mL) under a nitrogen atmosphere.
The resulting mixture was stirred at room temperature for 5 h
and then partitioned between CH2Cl2 and dilute hydrochloric
acid (2 M). The organic phase was washed with brine, dried
(MgSO4) and the solvent was evaporated in vacuo. The residual
crude compound S5 (1.16 g, 0.71 mmol) was redissolved in
CH2Cl2 (7 mL) and sealed under an atmosphere of nitrogen with
a rubber septum. Dimethylformamide (2 drops) was injected,
followed by the dropwise addition of oxalyl chloride (0.30 mL,
3.5 mmol). The resulting solution was stirred at room tempera-
ture for 35 min while maintaining a slow nitrogen flow above
the reaction by means of a syringe needle through the rubber
septum. The solvent and a majority of excess reagent was
removed by evaporation in vacuo and the residual reagent was
removed in vacuo with the aid of 1,2-dichloroethane. The crude
acid chloride product was immediately dissolved in CH2Cl2 (4
mL) and added dropwise to a stirred solution of 90-hydroxy-
1,3,3-trimethylspiro[indoline-2,30-[3H]naphtha[2,1-b][1,4]oxazine]
(0.241 g, 0.70 mmol) and triethylamine (0.20 mL, 1.40 mmol)
in CH2Cl2 (5 mL) under a nitrogen atmosphere. The resulting
mixture was stirred at room temperature for 22 h. The
solvent was evaporated in vacuo and the residue was
redissolved in CH2Cl2 and this solution was filtered through a
plug of cotton wool. The filtrate was purified by flash column
chromatography over silica gel. Elution with 50–100% CH2Cl2
in petroleum spirit (40–60 ꢀC) afforded the side product
1,3,3-trimethylspiro[indoline-2,30-naphtho[2,1-b][1,4]oxazine]-
90-yl methacrylate, 4, (0.171 g, 59%).
1H NMR (400 MHz, CDCl3) d 4.26 (t, J ¼ 4.76 Hz, 2H, CH2-3),
3.63 (t, J ¼ 4.76 Hz, 2H, CH2-4), 3.42 (t, J ¼ 6.95 Hz, 2H,
CH2-5), 3.22 (t, J ¼ 6.59 Hz, 2H, CH2-1), 2.72 (t, J ¼ 6.59 Hz,
2H, CH2-2), 1.61 (m, 2H, CH2-6), 1.31 (m, 4H, CH2-9,10), 0.88
(t, J ¼ 6.95 Hz, 3H, CH3-11), 0.53 (m, 4H, CH2-7,8), 0.07 (s,
approx. 80H, SiCH3) ppm.
Step 3
Triethylamine (8.53 g, 84.3 mmol) was added to a solution of
dried (2 h at 130 ꢀC under vacuum) 2,2-bis(hydroxymethyl)-
propionic acid (10.11 g, 75.4 mmol) in dry dichloromethane
under nitrogen. Compound S3 (10.14 g, 7.54 mmol, average
MW ¼ 1345) was added dropwise to the cooled solution and
then stirred at room temperature for 30 min. The solvent was
evaporated in vacuo and the residue was redissolved in
diethyl ether, washed four times with dilute aq. HCl, then
brine and dried with MgSO4. The solvent was evaporated, and
the crude product was purified by column chromatography
(silica gel, diethyl ether/hexane, 1:1 ! 4:1 ! neat ether).
Comments: Fractionation is achieved on the column due to the
distribution of PDMS chain lengths. The product elutes from
the column as a broad band with longer PDMS chain lengths
1H NMR (400 MHz, d6-acetone) d 8.28 (d, J ¼ 2.4 Hz, 1H),
7.90 (d, J ¼ 8.8 Hz, 1H), 7.82 (s, 1H), 7.82 (d, J ¼ 8.9 Hz,
1H), 7.25 (d, J ¼ 2.4 Hz, 1H), 7.23 (d, J ¼ 2.4 Hz, 1H), 7.18
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(dd, J ¼ 7.7, 1.2 Hz, 1H), 7.14 (dd, J ¼ 7.2, 0.8 Hz, 1H), 7.04
(d, J ¼ 8.9 Hz, 1H), 6.86 (dt, J ¼ 7.4, 0.8 Hz, 1H), 6.65 (d, J
¼ 7.8 Hz, 1H), 6.38 (m, 1H), 5.88 (m, 1H), 2.77 (s, 3H), 2.09
(m, 3H), 1.35 (s, 3H), 1.33 (s, 3H) ppm.
1H NMR analysis gave an average molecular weight (Mn) of
1685. 1H NMR (400 MHz, d6-acetone) d 6.07 (s, 1H), 5.64–
5.63 (m, 1H), 4.33 (s, 4H), 4.24–4.16 (m, 6H), 3.61 (t, J ¼
5.00 Hz, 2H), 3.42 (t, J ¼ 6.80 Hz, 2H), 2.61 (d, J ¼ 4.48 Hz,
8H), 1.95–1.90 (m, 3H), 1.69–1.58 (m, 3H), 1.38–1.25 (m,
8H), 0.90–0.83 (m, 4H), 0.61–0.56 (m, 4H), 0.15–0.08 (m,
SiCH3) ppm.
Further elution with 2–5% EtOAc in CH2Cl2 gave the desired
product compound 7, (0.313 g, 23%) as a viscous golden-
coloured oil.
Step 2
1H NMR (400 MHz, d6-acetone) d 8.24 (d, J ¼ 2.4 Hz, 1H),
7.89 (d, J ¼ 8.8 Hz, 1H), 7.83 (s, 1H), 7.81 (d, J ¼ 8.9 Hz,
1H), 7.21-7.13 (m, 3H), 7.05 (d, J ¼ 8.9 Hz, 1H), 6.86 (dt, J ¼
7.4, 0.7 Hz, 1H), 6.65 (d, J ¼ 7.7 Hz, 1H), 6.17 (m, 1H), 5.71
(m, 1H), 4.53 (s, 2H), 4.52 (s, 2H), 4.18 (m, 2H), 3.59 (m,
2H), 3.40 (t, J ¼ 6.8 Hz, 2H), 2.77 (s, 3H), 2.77–2.67 (m, 4H),
1.98 (m, 3H), 1.60 (m, 2H), 1.54 (s, 3H), 1.38–1.32 (m, 4H),
1.36 (s, 3H), 1.33 (s, 3H), 0.89 (m, 3H), 0.61–0.55 (m, 4H),
0.13–0.07 (m) ppm.
Compound S6 (0.40 g, 2.37 mmol, average MW ¼ 1685) was
dissolved in dry dichloromethane (8 mL) under nitrogen fol-
lowed by one small drop of dimethylformamide via syringe.
Oxalyl chloride (0.04 mL, 4.72 mmol) was then added in one
portion. The mixture was stirred at room temperature for 35
min. The solvent and the majority of the excess oxalyl chlo-
ride were removed by evaporation in vacuo with the residual
reagent removed in vacuo with the aid of dichloromethane.
The acid chloride product was immediately dissolved in dry
dichloromethane (2 mL) and added via syringe to a stirred
solution of 90-hydroxy-1,3,3-trimethylspiro[indoline-2,30-
[3H]naphth[2,1-b][1,4]oxazine] (0.086 g, 0.25 mmol) and
triethylamine (0.10 mL, 0.71 mmol) in dichloromethane (6
mL), under nitrogen. The resulting mixture was stirred at
room temperature for 4 h. The solvent was evaporated and
the residue was redissolved in chloroform and filtered
through a plug of silica. The crude product was purified by
flash column chromatography (100% CH2Cl2) giving 0.028 g
of the product, 8.
Spirooxazine Hetero Y-Branched
(Poly(dimethylsiloxane)/methacryloyloxyethyl
succinate) Conjugate, 8
1H NMR analysis gave an average molecular weight (Mn) of
1
1961. H NMR (200 MHz, d6-acetone) d 8.24 (d, 1H, J ¼ 2.40
Hz), 7.89 (d, 1H, J ¼ 8.80 Hz), 7.33–7.25 (m, 4H), 7.23–7.12
(m, 3H), 7.04 (d, 1H, J ¼ 8.80 Hz), 6.90–6.82 (m, 1H) 6.64
(d, 1H, J ¼ 7.70 Hz), 6.08–6.05 (m, 1H), 5.63–5.60 (m, 1H),
4.46 (s, 4H), 4.35 (s, 4H), 4.20–4.16 (m, 2H), 3.61–3.56 (m,
2H), 3.40 (t, 2H, J ¼ 6.80 Hz), 2.80–2.69 (m), 1.90–1.88 (m,
3H), 1.67–1.59 (m, 3H), 1.50 (s, 3H), 1.34 (d, 10H, J ¼ 4.30
Hz), 0.92–0.85 (m, 3H), 0.61–0.53 (m, 4H), 0.15–0.08 (m,
SiCH3) ppm.
a-Spirooxazine x-Methacrylate-Functionalized
Poly(dimethylsiloxane) Conjugate, 9
Compound 9 falls under the class of compound reported in
patent WO 2005/105875, Example 7.
Step 1
Compound 2 (0.91 g, 0.62 mmol, average MW ¼ 1473) was
dissolved in dry CH2Cl2 (8 mL) in an oven-dried Schlenk flask
under nitrogen. Triethylamine (0.26 mL, 1.86 mmol) and 4-
dimethylaminopyridine (2 mg) were added followed by the
addition of a solution of mono-2-(methacyloyloxy)ethyl succi-
noyl chloride (0.185 g, 0.74 mmol, see Step 1 in synthesis of
compound 5) in CH2Cl2 (1 mL). The mixture was stirred for 4
h at room temperature. Trigol monomethyl ether (21 mg, 0.12
mmol) was then added and the mixture was stirred for an
additional 1 h. The mixture was diluted with CH2Cl2 and
washed with 10 mL of 2 M HCl. The aqueous layer was
extracted with CH2Cl2 (2ꢁ 20 mL). The combined organic
layers were dried (MgSO4), and the solvent was evaporated.
The crude residue was purified by column chromatography
(silica gel, 10% ! 50% EtOAc/petroleum ether and then 6%
MeOH/CH2Cl2). A total yield of 0.730 g of S6 was obtained.
Step 1
Methacryloyl chloride (0.084 g, 0.80 mmol) was added drop-
wise via syringe to a solution of compound S7 (1.00 g,
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
0.80 mmol, Gelest, DMS-C15, Mn ¼ 1246) and triethylamine
(0.325 g, 3.21 mmol, 0.45 mL) in anhydrous diethyl ether
(15 mL). The mixture was stirred at room temperature for
30 min, under nitrogen. Succinic anhydride (0.08 g, 0.80
mmol) was added in one portion and the mixture was
stirred overnight. The solvent was evaporated and the resi-
due was purified by column chromatography (silica gel,
Et2O/hexane, 2:3 ! 1:1 ! 3:2). Of the several fractions col-
lected only the highest purity fraction of compound S8
(0.259 g) was selected and taken to the next step.
Naphthopyran Monomethacryloyloxyethyl Succinate, 11
This compound was synthesized in the same manner as
described for compound 5, using 2-phenyl-2-(4-dimethylami-
nophenyl)-5-hydroxymethyl-7,9-dimethoxy-2H-naphtho[1,2-b]
pyran (0.150 g, 0.32 mmol) in place of the spirooxazine. The
crude reaction product was purified by flash column chro-
matography, eluting with 100% CH2Cl2 ! 1% MeOH in
CH2Cl2 (0.068 g, 31%).
1H NMR (400 MHz, d6-acetone) d 7.66 (s, 1H), 7.57–7.55 (m,
2H), 7.37–7.32 (m, 4H), 7.27–7.22 (m, 2H), 6.97, (d, J ¼ 9.92
Hz, 1H), 6.66–6.63, (m, 2H), 6.57 (d, J ¼ 2.20 Hz, 1H), 6.38
(d, J ¼ 9.92 Hz, 1H), 6.07–6.06 (m, 1H), 5.61–5.60 (m, 1H),
5.27 (s, 2H), 4.34–4.30 (m, 4H), 3.95 (s, 3H), 3.93 (s, 3H),
2.86 (s, 6H), 2.64 (s, 4H), 1.90–1.89 (m, 3H) ppm.
Step 2
Oxalyl chloride (excess) was added to a solution of com-
pound S8 (0.259 g) and dimethylformamide (one small
drop) in anhydrous CH2Cl2 (10 mL). The mixture was stirred
at room temperature under nitrogen for 30 min. The solvent
and excess reagent were evaporated in vacuo and the resi-
due, compound S9, was redissolved in anhydrous CH2Cl2. To
this solution, 90-hydroxy-1,3,3-trimethylspiro[indoline-2,30-
[3H]naphtha[2,1-b][1,4]oxazine] (0.10 g, 0.29 mmol) was
added followed by triethylamine (excess). The mixture was
stirred at room temperature for 30 min and the solvent was
evaporated. The crude residue was purified by column
chromatography on silica gel to give 6 (average MW ¼ 1526,
nPDMS ¼ 10.4).
Naphthopyran Propionate, 12
This compound was synthesized in the same manner as
described for compound 6, using 2-phenyl-2-(4-dimethylami-
nophenyl)-5-hydroxymethyl-7,9-dimethoxy-2H-naphtho[1,2-b]
pyran (0.050 g, 0.11 mmol) in place of the spirooxazine
(yield: 0.054 g, 96%).
1H NMR (200 MHz, CDCl3) d 7.67 (s, 1H) 7.47–7.52 (m, 2H),
7.17–7.38 (m, 6H), 6.87 (d, J ¼ 10.0 Hz, 1H, pyran-CH), 6.74
(br s, 2H) 6.46 (d, J ¼ 2.0 Hz, 1H), 6.19 (d, J ¼ 10.0 Hz, 1H,
pyran-CH), 5.26 (s, 2H, ArCH2O), 3.93 (s, 3H, CH3O), 3.92 (s,
3H, CH3O), 2.93 (s, 6H, N(CH3)2), 2.36 (q, J ¼ 8.0 Hz, 2H,
propionyl-CH2), 1.14 (t, J ¼ 8.0 Hz, 3H, propionyl-CH3) ppm.
13C NMR (200 MHz, CDCl3) d 174.2, 158.5, 156.5, 147.3,
145.3, 128.7, 128.1, 127.9, 127.2, 126.7, 126.5, 125.9, 121.7,
120.2, 116.1, 115.8, 98.2, 92.5, 82.5, 64.6, 55.5, 27.7, 9.1
ppm.
1H NMR (400 MHz, d6-acetone) d 8.26 (d, 1H) 7.88 (d, 1H),
7.82 (s overlap, 1H), 7.80 (d overlap, 1H), 7.14–7.21 (m,
3H), 7.04 (d, 1H), 6.87 (m, 1H), 6.66 (d, 1H), 6.08 (m, 1H),
5.62 (m, 1H), 4.25 (m, 4H), 3.66 (m, 4H), 3.45 (t, 4H), 2.99
(t, 2H), 2.77–2.82 (m, 5H), 1.92 (s, 3H), 1.62 (m, 4H), 1.36
(s, 3H), 1.34 (s, 3H), 0.59 (m, 4H), 0.09–0.13 (m, SiCH3)
ppm.
Naphthopyran Hetero Y-Branched
(Poly(dimethylsiloxane)/methacryloyloxyethyl
succinate) Conjugate, 13
Spirooxazine Poly(dimethylsiloxane) Succinate
Conjugate, 10
This conjugate was synthesized in the same manner as
described for compound 8, using 2-phenyl-2-(4-dimethylami-
nophenyl)-5-hydroxymethyl-7,9-dimethoxy-2H-naphtho[1,2-b]
pyran in place of the spirooxazine in the final step. The
crude product was purified by flash column chromatography
eluting with 1% MeOH in CH2Cl2, giving a deep blue colored
gum.
A synthesis of this compound is outlined in patent WO
2004/041961; PCT/AU03/01453 (2003). It is synthesized
here using the following alternative procedure: Triethylamine
(0.54 g, 0.75 mL, 5.37 mmol) was added to a suspension of
90-hydroxy-1,3,3-trimethylspiro[indoline-2,30-[3H]naphth[2,1-
b][1,4]oxazine] (0.924 g, 2.68 mmol) in dry CH2Cl2 (15 mL)
under an argon atmosphere. Monoacid chloride-terminated
PDMS, S3, (ca. 2.44 mmol) was then added dropwise, and
the mixture was stirred at room temperature for 30 min.
The solvent was evaporated in vacuo; the residue redissolved
in a mixture of Et2O/hexane (1:1) and this solution filtered
through a plug of silica gel. The solvent was evaporated and
the oily residue was purified by column chromatography
(silica gel, Et2O/hexane, 1:3) to give the product, monospir-
ooxazine-terminated PDMS, 10, as a viscous green oil (2.92
g, 77%, average MW ¼ 1381, nPDMS ¼ 9.9).
1H NMR analysis gave an average molecular weight (Mn) of
1
2299 (nPDMS ¼ 17.1). H NMR (400 MHz, d6-acetone) d 7.66
(s, 1H), 7.58–7.56 (m, 2H), 7.37–7.31 (m, 4H), 7.27–7.21 (m,
2H), 6.98 (d, J ¼ 9.9 Hz, 1H), 6.66–6.64 (m, 2H), 6.57 (d, J ¼
2.6 Hz, 1H), 6.41 (d, J ¼ 9.9 Hz, 1H), 6.07 (m, 1H), 5.61–5.60
(m, 1H), 5.33–5.30 (m, 2H), 4.34–4.31 (m, 4H), 4.27–4.14
(m, 6H), 3.96 (s, 3H), 3.93 (s, 3H), 3.75 (t, J ¼ 5.0 Hz, 2H),
3.41 (t, J ¼ 6.84 Hz, 2H), 2.87 (s, 6H), 2.53–2.50 (m, 8H),
1.89 (s, 3H), 1.64–1.56 (m, 2H), 1.38–1.34 (m, 4H), 1.22 (s,
3H), 0.91–0.88 (m, 3H), 0.60–0.56 (m, 4H), 0.12–0.07 (m,
SiCH3) ppm.
1H NMR (200 MHz, d6-acetone) d 8.25 (d, 1H), 7.88 (d, 1H),
7.83 (s, 1H), 7.81 (d (overlapping), 1H), 7.18 (m, 3H), 7.04
(d, 1H), 6.86 (t, 1H), 6.66 (d, 1H), 4.25 (t, 2H), 3.65 (t, 2H),
3.44 (t, 2H), 2.99 (t, 2H), 2.80 (t (overlapping), 2H), 2.77 (s,
3H), 1.62 (m, 2H), 1.35 (m (overlapping), 10H), 0.89 (t, 3H),
0.59 (m, 4H), 0.10 (m, SiCH3) ppm.
Naphthopyran Poly(dimethysiloxane) Succinate
Conjugate, 14
This conjugate was synthesized in the same manner as
described for compound 10, using 2-phenyl-2-(4-
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ARTICLE
SCHEME 1 Synthesis of novel
hetero Y-branched photochromic
dye (spirooxazine) conjugates.
dimethylaminophenyl)-5-hydroxymethyl-7,9-dimethoxy-2H-naph-
tho[1,2-b]pyran in place of the spirooxazine.
that a monoprotection/deprotection scheme could be used, as
per the literature procedure,23 providing solely the monoacy-
lated derivative, increasing yields and eliminating wasteful by-
1H NMR (200 MHz, d6-acetone) d 7.67 (s, 1H), 7.60–7.55 (m,
2H), 7.38–7.20 (m, 6H), 6.99 (d, J ¼ 9.9 Hz, 1H, pyran-CH),
6.65 (m, 2H), 6.57 (d, J ¼ 2.6 Hz,1H), 6.38 (d, J ¼ 9.9 Hz,
1H, pyran-CH), 5.28 (s, 2H), 4.17 (m, 2H), 3.95 (s, 3H, OCH3),
3.93 (s, 3H, OCH3), 3.57 (m, 2H), 3.39 (t, J ¼ 6.8 Hz, 2H),
2.86 (s, 6H, NCH3), 2.68 (s, 4H, succinate-CH2), 1.60 (m, 2H),
1.38 (m, 4H, butyl-CH2), 0.91 (m, 3H, butyl-CH3), 0.59 (m,
4H, SiCH2), 0.14–0.10 (m, SiCH3) ppm.
product formation. Intermediate compound
2 was then
reacted with methacryloyl chloride or mono-2-(methacyloyloxy)
ethyl succinoyl chloride giving precursor 3, whose carboxylic
acid functionality was converted to an acid chloride using
oxalyl chloride with dimethylformamide as catalyst. Subse-
quent reaction with a hydroxyl-functionalized photochromic
dye, in this case 90-hydroxy-1,3,3-trimethylspiro[indoline-2,30-
3H-naphth[2,1-b][1,4]oxazine] and 2-phenyl-2-(4-dimethylami-
nophenyl)-5-hydroxymethyl-7,9-dimethoxy-2H-naphtho[1,2-
b]pyran, gave the corresponding conjugates 7, 8 (Table 1),
and 13 (Table 2). Even though acid chloride chemistry was
solely used to construct these architectures through ester
bonds, it is envisaged that similar results could be obtained
through the use of reagents such as dicyclohexylcarbodiimide
or (N-ethyl N-(dimethylaminopropyl)carbodiimide hydrochlor-
ide) with 4-dimethylaminopyridine (DMAP) catalyst to form
ester linkages in one step from the carboxylic acids and corre-
sponding alcohols.
RESULTS AND DISCUSSION
Synthesis
All of the photochromic conjugates and control compounds
synthesized for this study are listed in Tables 1 and 2. Het-
ero Y-branched conjugates were synthesized using readily
available 2,2-bis(hydroxymethyl)propionic acid, 1 (Scheme
1), as the Y-branching linker between the photochromic dye,
PDMS and methacrylate functionalities. Numerous examples
of its use, as well as other related difunctional structural
fragments, as Y-branching linkers in the synthesis of mik-
toarm star copolymers and dendrimers can be found in the
literature.23–31 This basic building block, with two equivalent
hydroxyl functionalities, was reacted with a monoacid chlo-
ride-functionalized PDMS oligomer in a 1:1 ratio, which
resulted in a statistical distribution of bisacylated, unacy-
lated, and monoacylated products, of which the latter, 2, was
isolated by silica gel column chromatography. We postulate
Evaluation of Photochromic Performance
The spirooxazine and naphthopyran photochromic control
compounds 6 and 12 are neither conjugated to PDMS nor do
they become bound to the matrix upon cure. These com-
pounds can be considered the benchmark for comparison
with all the other compounds tested here as they represent
the way photochromic dyes are usually incorporated within
current cast-in commercial photochromic lens products.
FAST SWITCHING IMMOBILIZED PHOTOCHROMIC DYES, MALIC ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
TABLE 3 Photokinetic Analysis of the Thermal Decoloration of Spirooxazine and
Naphthopyran Conjugates and their Corresponding Controls in Host Lens Matrix
Compounda
A0
A1
k1 (minꢂ1
)
A2
k2 (minꢂ1
)
Ath
t1/2 (s)
t3/4 (s)
b
4
0.687
0.730
0.968
0.716
1.160
1.161
1.019
0.305
0.735
0.640
0.778
0.431
0.512
0.620
0.620
0.671
0.739
0.886
0.422
0.529
0.503
0.629
0.575
1.112
2.139
2.555
2.732
3.378
5.537
0.204
0.320
0.642
0.788
0.355
0.293
0.229
0.219
0.197
0.162
0.083
0.299
0.255
0.310
0.239
0.049
0.066
0.082
0.084
0.086
0.105
0.147
0.018
0.023
0.039
0.043
0.104
0.061
0.040
0.042
0.033
0.029
0.008
0.180
0.155
0.136
0.094
170
53
996
361
135
152
99
5
6
22
7
20
8
18
9
13
48
10
11
12
13
14
a
8
19
583
280
175
93
4659
2465
1557
572
Compounds 4–10 monitored at 615 nm (kmax) and incorporated within lens matrix at 1.2 ꢁ 10ꢂ6 mol/g;
compounds 11–14 monitored at 585 nm (kmax) and incorporated at 1.5 ꢁ 10ꢂ7 mol/g.
b
Maximum measured absorbance intensity at onset of thermal decoloration period.
Compounds 4, 5, and 11 are methacrylate-functionalized
in table) to be reduced by half and three quarters, respec-
photochromic dyes which are included as controls to demon-
strate the effects of matrix tethering in combination with
spacer length on photochromic performance. Compounds 10
and 14 are unbound controls which serve to solely demon-
strate the effects of PDMS conjugation.
tively, during decoloration.
Spirooxazine Compounds
As expected, the methacrylate functionalization of the parent
spirooxazine photochromic dye to enable tethering to the
host matrix on cure, compounds 4 and 5, causes a significant
slowing of the thermal decoloration process when compared
with untethered control, 6. Compound 4 which has a meth-
acrylate functionality directly bound to the dye is the slower
of the two examples, with fade speed slowed by approxi-
mately 750% for t1/2 and t3/4 (Table 3). In comparison, com-
pound 5 having the ethoxysuccinate spacer between dye and
methacrylate moiety shows an improvement in fade speed
over compound 4, but is still markedly slower that the
untethered control 6 (t1/2 and t3/4 each slowed by about
250%). These results are quite consistent with previous
reports on photochromic dyes tethered to polymers which
state a dependence of linker length on decoloration perform-
ance, longer linkers providing faster decoloration perform-
ance due to the isolation of the photochromic moiety from
the steric influences of the main polymer chain.3,9–13
All compounds were incorporated within a standard thermoset
lens matrix formulation composed of four parts (by weight)
ethoxylated bisphenol A dimethacrylate (EO/phenol ¼ 1.3),
one part PEG 400 dimethacrylate and 0.4 wt % azobis(isobu-
tyronitrile) (radical initiator). The mixtures were added to a
mould and thermally cured. The test lenses thus obtained were
subjected to kinetic testing using a light table comprising a
UV–Vis spectrophotometer equipped with an external UV light
source. The samples were irradiated with filtered UV light
(350–400 nm) for a duration of 1000 s (coloration) at which
point the light source was turned off and the sample was fur-
ther monitored in the dark (decoloration). Monitoring was con-
ducted at kmax of the colored form of the photochromic.
The decoloration kinetics were analyzed using the following
empirical biexponential equation:
Conversely, the fastest spirooxazine compound, 10, is a non-
matrix tethered mono end-functionalized PDMS conjugate.
We have reported on the synthesis and photochromic prop-
erties of such conjugates previously, which provide unsur-
passed photochromic switching enhancement within a rigid
polymer matrix.14,18 Spirooxazine conjugate 10 shows a sub-
stantial improvement in fade speed compared with control
6, with a reduction in t1/2 from 22 to 8 s (64%) and a
reduction in t3/4 from 135 to 19 s (86%).
AðtÞ ¼ A1eꢂk t þ A2eꢂk t þ Ath
1
2
where A(t) is the optical density at kmax, A1 and A2 are con-
tributions to the initial optical density A0 (maximum attained
absorbance value at 1000 s UV irradiation), k1 and k2 are
the rates of the fast and slow components, respectively, and
Ath is the residual coloration (offset). The application of this
equation in analyzing the decoloration behavior of both spi-
rooxazines and naphthopyrans in solid media has previously
been demonstrated.14–16,32–35 Spectrokinetic data for all com-
pounds tested are presented in Table 3. This table also
includes values of t1/2 and t3/4 which are defined as the
time taken for the initial absorbance value, A0 (also included
Conjugates 7 and 8 which bear both matrix tethering meth-
acrylate functionality and fade speed improving PDMS
oligomer are essentially a compromise between the two
aforementioned control compound types. Conjugate 7 bears
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WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
decreases, indicating that decoloration is progressively mov-
ing towards a monoexponential decay pattern as fade speed
increases. In addition, the faster conjugates generally become
darker under UV irradiation, as denoted by A0, and possess a
lower residual coloration, Ath. The kinetic plots of each spi-
rooxazine compound during the first 5 min of decoloration
are shown in Figure 3.
Naphthopyran Compounds
The naphthopyran compounds synthesized here are based
on a slower performing parent photochromic dye compared
with the spirooxazine. In addition, naphthopyrans generally
possess greater residual coloration, Ath, due to the existence
of a relatively thermally stable isomer of the colored open
form,5,16–18,36–39 which was observed in our experiments
(Table 3). Despite these inherent differences between the
two photochromic types, we observed similar trends in the
spectrokinetic data for naphthopyran compounds 11–14 (Ta-
ble 3). Here we also analyzed the photochromic kinetics
through fitting our decoloration curves with the above biex-
ponential equation, which gave good correlations coefficients
(R) in excess of 0.99.
FIGURE 3 Plots of the first 5 min of decoloration of spirooxa-
zine conjugates and control compounds 4–10. (‘‘Bound’’ refers
to the dye being covalently bound to the host matrix).
Matrix tethered compound 11 was the slowest of all four
compounds tested. The benchmark untethered control com-
pound 12 was significantly faster, with both t1/2 and t3/4 val-
ues approximately halved. The hetero Y-branched compound
13 with both fade speed enhancing PDMS and matrix tether-
ing methacrylate moieties was able to outperform the
unbound control compound 12 in decoloration. Finally, and
as expected, the untethered naphthopyran–PDMS control
conjugate 14 was the fastest. The kinetic plots of the first 5
a methacrylate functionality which is appended very close to
the photochromic moiety and performs similarly to unteth-
ered control compound 6 (Table 3). It can be viewed here
that the PDMS basically cancels the effect of matrix tethering.
Using a slightly longer linker between the photochromic and
methacrylate functionality in this type of system, as seen in
conjugate 8, further betters fade performance where now we
are able to produce faster fade speeds than the untethered
control 6 while having the dye tethered to the matrix. This
is the first demonstration of a matrix-bound photochromic
dye switching faster than its electronically identical unbound
analogue within the same matrix.
To further explore matrix tethering in combination with
PDMS conjugation, we synthesized conjugate 9, comprised of
a linear PDMS chain with photochromic dye and methacry-
late functionality at opposite termini. Here the methacrylate
functionality is well spaced from the photochromic (a linker
of approximately 40 linear chain covalent bonds), so not sur-
prisingly presents with the fastest fade speed enhancement
of all the matrix tethered compounds in this study. It is
interesting to note that despite this large separation and the
soft PDMS segment being between the photochromic and
methacrylate moieties, a distinct effect on fade speed per-
formance compared with the untethered spirooxazine–PDMS
conjugate 7 is still observed. Tethered PDMS conjugate 9 is
5 s slower to t1/2 and 29 s slower to t3/4. Tethering in this
type of configuration can be seen as reducing the effective
length of the PDMS chain.
The spectrokinetic data of these spirooxazine compounds, or-
dered from slowest to fastest, are presented in Table 3. As
expected, the rate constants of the fast and slow components
of decoloration, k1 and k2 respectively, follow an increasing
trend. We also observe that A1 is increasing while A2
FIGURE 4 Plots of the first 10 min of decoloration of Naphtho-
pyran conjugates and control compounds 11–14. (‘‘Bound’’
refers to the dye being covalently bound to the host matrix).
[Color figure can be viewed in the online issue, which is avail-
able at wileyonlinelibrary.com.]
FAST SWITCHING IMMOBILIZED PHOTOCHROMIC DYES, MALIC ET AL.
485

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
16 Malic, N.; Campbell, J. A.; Evans, R. A. Macromolecules
min of decoloration for naphthopyran conjugates and con-
trols are shown in Figure 4.
2008, 41, 1206–1214.
17 Ercole, F.; Malic, N.; Harrisson, S.; Davis, T. P.; Evans, R. A.
CONCLUSIONS
Macromolecules 2010, 43, 249–261.
We have devised a method of tethering photochromic dyes
to a host matrix while allowing uncompromised switching
performance. We have achieved the first example where a
photochromic dye bound to a rigid host matrix is able to
fade faster than its electronically equivalent unbound analog.
The faster fade speeds were attained in a novel conjugate
system comprising a photochromic dye attached to a PDMS
oligomer and a polymerizable methacrylate functionality
through a Y-branching linker. Further enhancement of fade
speed was achieved by the use of a longer linker between
the methacrylate functionality and the photochromic dye. To
this effect, we postulate that modulation may also be
achieved through modification of the PDMS chain length and
the use of alternative soft oligomers.
18 Ercole, F.; Malic, N.; Davis, T. P.; Evans, R. A. J Mater Chem
2009, 19, 5612–5623.
19 Kakishita, T.; Matsumoto, K.; Kiyotsukuri, T. J Heterocyclic
Chem 1992, 29, 1709–1715.
20 Breyne, O.; Chan, Y. Naphthopyran Derivatives, Composi-
tions and (Co)polymer Matrices Containing Same, U.S. Patent
6,399,791, June 4, 2002.
21 Evans, R. A.; Skidmore, M. A.; Yee, L. H.; Hanley, T. L.; Lewis,
D. A. Photochromic Compositions and Light Transmissible
Articles, Patent Application WO 2004/041961 A1, May 21, 2004.
22 HCl formed during the reaction cleaves the ether linkage and the
PDMS chain. An argon flow above the vigorously stirred reaction
mixture may assist in the removal of gaseous HCl as it is formed.
The authors would like to thank Advanced Polymerik, The Co-
operative Research Centre for Polymers and CSIRO Materials
Science and Engineering for supporting this work.
˚
23 Heise, A.; Trollsas, M.; Magbitang, T.; Hedrick, J. L.; Frank,
C. W.; Miller, R. D. Macromolecules 2001, 34, 2798–2804.
24 Magnusson, H.; Malmstrom, E.; Hult, A. Macromolecules
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